Drive mechanism for opening rollers

ABSTRACT

A drive mechanism for the opening rollers of a row or two opposite rows of spinning units of a spinning machine, in which a common drive shaft extends longitudinally through the machine and carries a separate drive pulley for the opening roller of each spinning unit or for the opening rollers of two opposite spinning units, and in which this drive pulley is connected to the driving whirl of the opening roller of one or two opposite spinning units by guide or tension rollers.

United States Patent [191 Stahlecker DRIVE MECHANISM FOR OPENING ROLLERS [75] Inventor: Fritz Stahlecker, Bad Uberkingen,

Germany [73] Assignee: Wilhelm Stahlecker GmbH,

Reichenbach, Germany 221 Filed: Aug. 10, 1971 21 Appl. No.: 170,571

[30] Foreign Application Priority Data Aug. 17, 1970 Germany 2040636 [52] US. Cl 57/105, 57/5895, 74/242.l R [51] Int. Cl. D01h 1/20, Dolh l/l2 [58] Field of Search. 74/242.8, 242.11 R, 242.13 R, 74/221, 242.12, 242.15 R, 227, 242.5, 2428-2429, 242.1 R, 242.1 A, 242.1 TA,

[56] References Cited UNITED STATES PATENTS 422,155

2/1890 Priestman 57/105 [1111 3,802,176 [451 Apr. 9, 1974 510,694 12/1893 Marsh 74/221 2,014,397 9/1935 ,Smith 74/242.11 R 3,648,450 3/1972 Prochazka et a1. 57/5889 500,579 7/1893 lde 74/242.11 R X 1,406,933 2/1922 Cohn 74/221 3,224,180 12/1965 Graf 74/2427 X 3,120,732 2/1964 Stahlecker et a1. 57/105 3,668,854 6/1972 Le Chatelier 57/105 X Primary Examiner-John W. Huckert Assistant Examiner-Charles Gorenstein Attorney, Agent, or Firm-Craig and Antonelli [5 7 ABSTRACT A drive mechanism for the opening rollers of a row or two opposite rows of spinning units of a spinning machine, in which a common drive shaft extends longitudinally through the machine and carries a separate drive pulley for the opening roller of each spinning unit or for the opening rollers of two opposite spinning units, and in which this drive pulley is connected to the driving whirl of the opening roller of one or two opposite spinning units by guide or tension rollers.

5 Claims, 9 Drawing Figures {i I m aiiza! INVENTOR 1 FR TZ STAHLECKER ATTORNFYD PATENTEB P 9 I974 sum 2 or z INVENTOR FRITZSTAHLECKER BY -%,Gu auLL 6' 144,02

ATTORNEYEI DRIVE MECHANISM FOR OPENING ROLLERS The present invention relates to a drive mechanism for opening rollers of open-end spinning units, which rollers are mounted in the yarn-guide housing parts of the spinning units and the shafts of which carry driving whirls which are driven by belts or the like.

For driving opening rollers it is conventional as disclosed, for example, by the British patent No. 1084,664 to provide a tangential belt which runs through the entire spinning machine in the longitudinal direction thereof and drives the opening rollers through auxiliary shafts and additional gears which are associated with each spinning unit. Such a tangential belt drive is very susceptible to trouble and at a breakage of the belt all spinning units are stopped. Furthermore, the additional transmitting means are rather expensive and take up considerable space.

It is an object of the present invention to provide a drive mechanism for opening rollers of the type as first mentioned above which is of a very simple construction and may be easily operated, serviced and supervised.

For attaining this object, the invention provides a drive shaft which extends in the longitudinal direction of the spinning machine and is provided with drive pulleys for individual belts or the like each of which drives only one or no more than two driving whirls and is guided by at least one guide and/or tension roller. it is a particular advantage of the invention over the prior art that by means of an individual belt it is possible to bridge the gap between the drive shaft and the opening roller of each spinning unit withoutany additional expensive transmitting means.

The drive shaft may be mounted in a very desirable position, and according to one preferred embodiment of the invention it is mounted underneath the spinning rotors or turbines, preferably within the supporting structure thereof. For insuring a high safety of operation it is desirable that each individual belt drives only one opening roller since at the breakage of one of these belts only one spinning unit will be stopped. Especially for economical reasons it is, however, advisable to employ each individual belt for driving two opening rollers which are located on different sides of the machine. This embodiment of the invention which is based upon the advantageous location of the drive shaft has the advantage that it reduces the number of tension or guide rollers which are required for each individual belt.

It is another feature of the invention that the individual belts may be very easily installed and exchanged by pressing each belt by means of a tension or guide roller against the drive pulley without requiring the belt to be looped completely around this pulley. The looping angle on the drive pulley may also be made very small without requiring any excessive belt tension. For making the belt tension as small as possible, another embodimcnt of the invention provides that each individual belt is pressed by one tension or guide roller against the drive pulley and by another against the driving whirl without passing completely around either the drive pulley or the whirl. It has further been found to be of advantage to provide a tension or guide roller directly adjacent to the drive pulley and possibly also another tension or guide roller directly adjacent to the driving whirl. In order to prevent the yarn-guide housing or the turbine or rotor housing from being damaged by a violent deflection of the tension roller when an individual belt suddenly breaks, it is advisable to provide suitable stops for limiting the swinging movement of the tension roller.

For repairing a thread breakage or for cleaning the spinning turbine or rotor, it is already known to provide a spinning unit with a stationary turbine housing and its supporting structure and with a yarn-guide housing which may be removed from the stationary turbine housing by pivoting or sliding it away from it. For a spinning unit of this type of construction the present invention may be employed with a. very particular advantage since, especially if the individual belts are only pressed from the outside against the drive whirl or against the drive pulleys of the drive shaft, either the yarn-guide housing together with the drive means may be easily removed from the drive shaft or the driving whirl from the drive means without requiring the driving operation to be interrupted. For this purpose, it is provided in one embodiment of the invention that the tension and guide rollers be mounted on the stationary turbine housing or on the supporting structure thereof, while in another embodiment of the invention at least one tension or guide roller is provided on the yarnguide housing. Similar advantages will also be attained if the yarn-guide housing is mounted in a stationary position and the turbine housing is movable or if both housing parts are movable inorder to permit the spinning unit to be opened.

Another embodiment of the invention provides the individual belt to pass completely around the driving whirl and to permit it to he slipped laterally over the whirl after the spinning unit has been opened. This means that in this case the driving whirl is freely movable on the shaft of the opening roller. The drive belts generally consist of light and only slightly elastic bands. It may, however, also be of advantage to employ highly elastic bands because it is then possible to omit tension rollers and thereby to reduce the cost of the drive means considerably.

If the turbines of the two sides of the machine do not have to be located directly opposite to each other, it is another feature of a further embodiment of the invention that the individual belts of the opposite opening rollers which are driven by a common drive shaft are driven by a common drive pulley. i

All of the embodiments of the invention in which the opening rollers at the opposite sides of the machine are driven by a common drive shaft have in common that either one individual belt engages upon thedrive whirl of an opening roller, while another individual belt surrounds the drive whirl of the other opening roller, as shown in FIG. 6 so that both opening rollers will be driven in opposite directions, as may be seen in FIG. 7. For insuring that both drive whirls will be driven sub stantially equally by the same belt, it is another feature of the invention that directly adjacent to the whirl around which the individual belt is looped, a tension or guide roller be provided in such a manner that the looping angle on this whirl will correspond substantially to the looping angle on the opposite whirl around which the belt is not looped.

The yarn-guide housing of each spinning unit is in ad dition generally provided with at least one feed roller which must likewise be driven. It is for this purpose an additional feature of the invention that the main drive shaft also drives the delivery rollers "which are mounted on the yarn-guide housings by means of intermediate drive means, for example, by a gear-wheel transmission. This feature is also very advantageous since by only requiring a single drive shaft the entire structure is considerably more simplified and less expensive.

The various features of the present invention will become more clearly apparent from the following detailed description thereof which is to be read with reference to the accompanying drawings, in which FIG. 1 shows diagrammatically a side view of one embodiment of the invention;

FIG. 2 shows a top view of the drive mechanism according to FIG. 1;

FIG. 3 shows a side view of the drive mechanism according to FIG. 1 when the yarn-guide housing is pivoted to its open position;

FIG. 4 shows a diagrammatic illustration of another embodiment of the invention;

FIG. 5 shows a diagrammatic illustration of a further embodiment of the invention;

FIG. 6 shows a top view of a further embodiment of 20 the invention;

FIG. 7 shows a diagrammatic illustration of a drive mechanism according to the invention in which two opposite opening rollers are driven by a common belt;

FIG. 8 shows a view of a modification ofa part of the mechanism according to FIG. 7; while FIG. 9 shows a further embodiment of a drive mechanism according to the invention which is provided with an additional drive for a delivery roller.

Referring to FIGS. 1 to 3 of the drawings, the spinning unit comprises a yarn-guide housing 1 of which only the outline is shown and an opening roller 2 in this housing. Behind this housing 1 the turbine or rotor housing 3 of the spinning unit is located which is mounted on a supporting bracket 4. The turbine housing 3 contains the bearing and the drive means (not shown) of the spinning turbine or rotor 5. The yarnguide housing 1 is pivotable about a pin 6 on the supporting bracket 4 away from the turbine housing 3. In the bracket 4 a drive shaft 7 is mounted which extends in the longitudinal direction of the machine which comprises many spinning units of the same construction. Drive shaft 7 carries the drive pulleys 8 each of which drives a belt 9 which is pressed against its peripheral surface. The outer side of this belt 9 engages tightly upon a driving whirl 10 of the opening roller 2 and is adapted to drive the latter. Directly above the driving whirl 10 a guide roller 11 is located which is mounted on an arm 12 which is secured to the turbine housing 3. Belt 9 is tightened by a tension roller 13 which is located directly underneath the drive pulley 8 and is mounted on an arm 14 which is pivotably mounted on bracket 4 or on a supporting bar extending through the machine. This pivotable arm 14 is acted upon by a tension spring 15 which tends to pull the tension roller 13 away from the drive pulley 8.

FIG. 3 illustrates the spinning unit according to FIGS. 1 and 2 in the position in which the yarn-guide housing 1 is pivoted away from the turbine housing 3 and is thus in its open position. Since the individual belt 9 only engages upon the outside of the driving whirl 10 of the opening roller 2, the latter can be easily pivoted together with the yarn-guide housing 1 while belt 9 may continue to run without interference. Under the action of tension spring 15, arm 14 together with tension roller 13 will then be pivoted for a short distance away from the drive pulley 8. In order to permit the looping angle of belt 9 to be changed under which this belt engages upon the whirl 10 of the opening roller 2, arm 12 carrying the guide roller 11 is secured to the turbine housing 3 so as to be slidably adjustable in a substantially horizontal direction by a slot connection I6. The particular advantage of this construction of the driving means for the opening roller 2 is its great simplicity and reliability and the possibility of mounting the drive shaft in the most suitable position. Furthermore, when the guide element 1 is pivoted away from the turbine housing 3, the opening roller 2 will be stopped without requiring any brake to act upon the belt 9 or the belt to be lifted off the drive pulley 8. Each spinning unit of the machine may therefore be opened individually without affecting the continued drive of all other spinning units.

The embodiment of the invention as illustrated in FIG. 4 is generally similar to that as shown in FIGS. 1 to 3. However, in place of a tension roller 13 underneath the drive pulley 8 a guide roller 18 is mounted in a fixed position on a bearing bracket 17, and a tension roller 19 is mounted directly above the opening roller 2 with a driving whorl 10 on a pivotable arm 20 which forms a part of a two-armed lever the other end of which is acted upon by a tension spring 21 so that the tension roller 19 tends to pivot away from the opening roller 2 and the whirl 10. In order to prevent any damage in the event of a breakage of belt 9 and a resulting excessive deflection of tension roller 19, a pair of stops 22 and 23 are provided which limit the extent of the pivoting movement of arm 20. Of course, such stops 22 and 23 may also be provided for the tension rollers of all other embodiments of the invention.

In the further embodiment of the invention as shown in FIG. 5, the yarn-guide housing 24 is slidable in a horizontal direction away from the turbine housing 25 along a base 26. The opening roller 2 on the yarn-guide housing 24 is also in this case driven by an individual belt 27 by means of a common drive shaft 7 which extends in the longitudinal direction of the machine. Belt 27 is pressed against the peripheral surface of pulley 8 on drive shaft 7 and passes around the driving whirl 10 of the opening roller 2. Belt 27 which in this embodiment of the invention preferably consists of a highly elastic material is slipped from the side over the whirl 10 when the latter is accessible because the yarn-guide housing 24 is shifted outwardly or because a cover plate on the latter has been removed. Underneath the drive pulley 8 a guide roller 28 is mounted on a bracket 30 which is secured to the yarn-guide housing 24. If in this embodiment the yarn-guide housing 24 is shifted horizontally, belt 27 and thus also the opening roller 2 will be stopped. If instead of a highly elastic belt 27 an only slightly elastic belt is employed, it is advisable to mount the roller 28 on one end of a two-armed lever 30b which is pivotable about an axis 30a and the other end of which is acted upon by a tension spring 29 so that roller 28 then acts on the belt 27 as a tension roller.

The driving mechanism according to the invention may be simplified in the manner as shown in FIG. 6 by providing on drive shaft 7 a common drive pulley 35 which has at least twice the width as the pulleys of the embodiments as previously described and carries two individual belts 33 and 34 which run over two opposite driving whirls 10 of the opening rollers 2. In this case, the turbines 31 and 32 are laterally offset relative to each other. A drive mechanism of this type may also be applied with considerable advantage to open-end spinning machines. In this embodiment as shown in FIG. 6 it is assumed that the spinning units at the left and right sides of the machine are substantially of the same construction in which the turbine 31 is located at the left of the opening roller 2, as seen from the front of either side of the machine. If the spinning units of both rows would be designed symmetrically relative to the central longitudinal plane of the machine, a driving mechanism as illustrated in FIG. 6 would result in an arrangement in which the spinning turbines or both sides of the machine will be located almost exactly opposite to each other insofar as they would be offset from each other only to the extent of the width of one of the individual belts 33 and 34 plus an allowance of a small distance of, for example, 3 mm between the two adjacent belts.

FIG. 7 illustrates two opening rollers 2 which are disposed directly opposite to each other on both sides of the machine and aredriven by a single endless belt 36 which runs over a common pulley 8 on a common drive shaft 7. For attaining the proper direction of rotation of both opening rollers 2, as indicated by the arrows, the belt 36 must pass around one driving whirl 10, while the other driving whirl engages upon the outer side of belt 36. Thus, for example, belt 36 passes around whirl 10 of the opening roller at the left side of the drawing and engages upon the outside of the whirl of the opening roller at the right side. Shortly behind this whirl 10 a guide roller 11 is mounted in a similar manner as shown in FIG. 1. Belt 36 is tightened by a tension roller 37 which is mounted underneath the drive pulley 8 on an arm 39 which a tension spring 38 tends to pivot in the downward direction. If instead of looping the belt about an angle of 180 around one whirl 10 and engaging it at a looping angle of about to 40 with the other whirl 10 in the manner as shown in FIG. 7, the belt should engage at approximately the same small looping angle with both whirls 10, another guide roller 40 may be provided as shown in FIG. 8 which is mounted above the left whirl 10.

FIG. 9 finally shows an embodiment of the invention in which the drive pulley 8 which is secured to drive shaft 7 is located further toward the edge of the housing 1 than in FIG. 1, so as to be nearly vertically below the drive whorl 10 of the opening roller 2 and may thus press from the outside against the same side of a belt 54 against which the driving whirl 10 of the opening roller 2 is pressed. Belt 54 is running between and around two guide rollers 55 and 56 which may be mounted and arranged in a similar manner as in some of the embodiments of the invention as previously described. The drive shaft 7 of this embodiment according to FIG. 9 is also utilized for driving a feed roller 57 which is mounted in the yarn-guide housing, not shown, preceding the opening roller 2. Drive shaft 7 is for this purpose provided in each spinning unit with a worm gearing 58 and 59 which is connected through a shaft 60 to a worm gearing 6.1 and 62 of the delivery roller 57.

In all of the embodiments of the invention as illustrated it is advisable to provide the individual belts in the form of light bands or belts which may be easily removed and replaced at any time. It is therefore preferable to design the drive units so that these bands or belts are not wound around the drive pulleys 8 on drive shaft 7 so as to envelop the same. These bands or belts are preferably so-called adhesion bands which are impregnated on one or both sides, but they may also be uncoated. In certain cases it is advisable to employ highly elastic bands or belts, for example, when by pivoting or sliding the yarn-guide housing away from the turbine housing or vice versa the tension rollers must carry out very large movements. If such highly elastic hands or belts are employed, the tension rollers may also be omitted entirely as shown, for example, in FIG. 5.

Finally it may be mentioned that when the respective spinning unit according to the invention is opened, the individual band or belt is loosened entirely or almost entirely from the driving whirl or the drive pulleys so that the opening roller will be stopped completely. If such stopping should occur very quickly, it is, of course, possible to provide suitable brake means which act upon the driving whirl of the opening roller or directly upon the latter while the spinning unit is being opened or after it has been opened.

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, I wish to have it understood that it is in no way limited to the details of such embodiments but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed my invention, what I claim is:

l. A drive mechanism for the opening rollers of openend spinning units of a spinning machine, in which each unit has a housing having two parts, one of said parts being stationary and the other part being movable relative to said stationary part for opening and closing said housing, a spinning turbine mounted in said stationary housing part, an opening roller rotatably mounted in said movable housing part, and a driving whirl for said opening roller and connected thereto, a common drive shaft on said stationary housing part and extending longitudinally through said machine for driving the opening rollers of all spinning units, a drive pulley secured to said drive shaft, tension roller means mounted in at least one of said housing parts, and an individual endless belt adapted to run over said drive pulley, said tension roller means and said driving whirl for driving said opening roller of said spinning unit, and further in which each belt is pressed by one roller of said tension roller means against said drive pulley without passing around the same.

2. A drive mechanism for the opening rollers of openend spinning units ofa spinning machine, in which each unit has a housing having two parts, one of said parts being stationary and the other part being movable relative to said stationary part for opening and closing said housing, a spinning turbine mounted in said stationary housing part, an opening roller rotatably mounted in said movable housing part, and a driving whirl for said opening roller and connected thereto, a common drive shaft on said stationary housing part and extending longitudinally through said machine for driving the opening rollers of all spinning units, a drive pulley secured to said drive shaft, tension roller means mounted in at least one of said housing parts, and an individual endless belt adapted to run over said drive pulley, said tension roller means and said driving whirl for driving said opening roller of said spinning unit, and further in which each belt is pressed by one roller of said tension roller means against said drive pulley and by another of said rollers against said driving whirl without passing around said pulley and said whirl.

3. A drive mechanism for the opening rollers of openend spinning units of a spinning machine, in which each unit has a housing having two parts, one of said parts being stationary and the other part being movable relative to said stationary part for opening and closing said housing, a spinning turbine mounted in said stationary housing part, an opening roller rotatably mounted in said movable housing part, and a driving whirl for said opening roller and connected thereto, a common drive shaft on said stationary housing part and extending longitudinally through said machine for driving the opening rollers of all spinning units, a drive pulley secured to said drive shaft, tension roller means mounted in at least one of said housing parts, and an individual endless belt adapted to run over said drivey pulley, said tension roller means and said driving whirl for driving said opening roller of said spinning unit, and further in which each of said individual belts is adapted to drive the driving whirls of two opening rollers located on the opposite side of said machine, and further in which said tension roller means comprise a first roller mounted underneath said drive pulley and a second roller closely adjacent to said driving whirl of one of said opening rollers, said belt passing around a sector of said drive pulley, then toward and almost completely around one of said driving whirls, then toward and around a sector of said first roller, then toward and around a sector of the second driving whirl, then toward and almost completely around said second roller, and then again to said drive pulley.

4. A drive mechanism for the opening rollers of openend spinning units of a spinning machine, in which each unit has a housing having two parts, one of said parts being stationary and the other part being movable relative to said stationary part for opening and closing said housing, a spinning turbine mounted in said stationary part, an opening roller rotatably mounted in said movable housing part, and a driving whirl for said opening roller and connected thereto, a common drive shaft on said stationary housing part and extending longitudinally through said machine for driving the opening rollers of all spinning units, a drive pulley secured to said drive shaft, tension roller means mounted in at least one of said housing parts, and an individual endless belt adapted to run over said drive pulley, said tension roller means and said driving whirl for driving said opening roller of said spinning unit, and further in which each of said individual belts is adapted to drive the driving whirls of two opening rollers located on the opposite sides of said machine, and further in which said tension roller means comprise a first roller mounted underneath said drive pulley, a second roller mounted closely adjacent to the driving whirl of a first of said opening rollers, and a third roller mounted closely adjacent to the driving whirl of the second opening roller, said belt passing around only a sector of said drive pulley, then toward and only around a sector of one of said whirls, then almost completely around said second roller, then toward and around a sector of said first roller, then toward and only around a sector of the other whirl, the almost completely around said third roller and then again to said drive pulley.

5. A drive mechanism as defined in claim 4, in which the sectors of engagement of said belt with said two whirls have substantially the same angle of contact. 

1. A drive mechanism for the opening rollers of open-end spinning units of a spinning machine, in which each unit has a housing having two parts, one of said parts being stationary and the other part being movable relative to said stationary part for opening and closing said housing, a spinning turbine mounted in said stationary housing part, an opening roller rotatably mounted in said movable housing part, and a driving whirl for said opening roller and connected thereto, a common drive shaft on said stationary housing part and extending longitudinally through said machine for driving the opening rollers of all spinning units, a drive pulley secured to said drive shaft, tension roller means mounted in at least one of said housing parts, and an individual endless belt adapted to run over said drive pulley, said tension roller means and said driving whirl for driving said opening roller of said spinning unit, and further in which each belt is pressed by one roller of said tension roller means against said drive pulley without passing around the same.
 2. A drive mechanism for the opening rollers of open-end spinning units of a spinning machine, in which each unit has a housing having two parts, one of said parts being stationary and the other part being movable relative to said stationary part for opening and closing said housing, a spinning turbine mounted in said stationary housing part, an opening roller rotatably mounted in said movable housing part, and a driving whirl for said opening roller and connected thereto, a common drive shaft on said stationary housing part and extending longitudinally through said machine for driving the opening rollers of all spinning units, a drive pulley secured to said drive shaft, tension roller means mounted in at least one of said housing parts, and an individual endless belt adapted to run over said drive pulley, said tension roller means and said driving whirl for driving said opening roller of said spinning unit, and further in which each belt is pressed by one roller of said tension roller means against said drive pulley and by another of said rollers against said driving whirl without passing around said pulley and said whirl.
 3. A drive mechanism for the opening rollers of open-end spinning units of a spinning machine, in which each unit has a housing having two parts, one of said parts being stationary and the other part being movable relative to said stationary part for opening and closing said housing, a spinning turbine mounted in said stationary housing part, an opening roller rotatably mounted in said movable housing part, and a driving whirl for said opening roller and connected thereto, a common drive shaft on said stationary housing part and extending longitudinally through said machine for driving the opening rollers of all spinning units, a drive pulley secured to said drive shaft, tension roller means mounted in at least one of said housing parts, and an individual endless belt adapted to run over said drivey pulley, said tension roller means and said driving whirl for driving said opening roller of said spinning unit, and further in which each of said individual belts is adapted to drive the driving whirls of two opening rollers located on the opposite side of said machine, and further in which said tension roller means comprise a first roller mounted underneath said drive pulley and a second roller closely adjacent to said driving whirl of one of said opening rollers, said belt passing around a sector of said drive pulley, then toward and almost completely around one of said driving whirls, then toWard and around a sector of said first roller, then toward and around a sector of the second driving whirl, then toward and almost completely around said second roller, and then again to said drive pulley.
 4. A drive mechanism for the opening rollers of open-end spinning units of a spinning machine, in which each unit has a housing having two parts, one of said parts being stationary and the other part being movable relative to said stationary part for opening and closing said housing, a spinning turbine mounted in said stationary part, an opening roller rotatably mounted in said movable housing part, and a driving whirl for said opening roller and connected thereto, a common drive shaft on said stationary housing part and extending longitudinally through said machine for driving the opening rollers of all spinning units, a drive pulley secured to said drive shaft, tension roller means mounted in at least one of said housing parts, and an individual endless belt adapted to run over said drive pulley, said tension roller means and said driving whirl for driving said opening roller of said spinning unit, and further in which each of said individual belts is adapted to drive the driving whirls of two opening rollers located on the opposite sides of said machine, and further in which said tension roller means comprise a first roller mounted underneath said drive pulley, a second roller mounted closely adjacent to the driving whirl of a first of said opening rollers, and a third roller mounted closely adjacent to the driving whirl of the second opening roller, said belt passing around only a sector of said drive pulley, then toward and only around a sector of one of said whirls, then almost completely around said second roller, then toward and around a sector of said first roller, then toward and only around a sector of the other whirl, the almost completely around said third roller and then again to said drive pulley.
 5. A drive mechanism as defined in claim 4, in which the sectors of engagement of said belt with said two whirls have substantially the same angle of contact. 